We have recently demonstrated that the bitter taste receptor T2R38 is expressed in the upper airway and is activated by acyl-homoserine lactones (AHLs): quorum-sensing molecules secreted by Pseudomonas aeruginosa and other gram-negative bacteria. Furthermore, we found that T2R38 regulates human upper airway innate defenses through nitric oxide production, which stimulates mucociliary clearance and has direct antibacterial effects. Moreover, common polymorphisms of the TAS2R38 gene, correlating with taste sensitivity to the molecule PTC, are linked to significant differences in the ability of uppe respiratory cells to clear and kill bacteria in response to AHLs. Based on these results, our central hypothesis is that the bitter taste receptor T2R38 expressed in the upper respiratory epithelium constitutes a sentinel defense network for the detection and clearance of microbes and that genetic variation in T2R38 contributes to individual differences in airway defensive capabilities. To test this hypothesis, we will: (1) determine whether TAS2R38 genotype, PTC taste sensitivity, and allele-specific expression correlate with symptom severity, disease burden, and interventional outcomes of chronic rhinosinusitis (CRS), and whether TAS2R38 polymorphisims not activated by AHLs are overrepresented in a cohort of CRS patient, and (2) identify other micorbial products that activate the common genetic variants of TAS2R38. The goal of these aims is to determine the role the bitter taste receptor T2R38 plays in upper airway defense and how common polymorphisms of this receptor contribute to upper airway disease. Furthermore, we will determine whether bitter taste sensitivity can be used as an indicator for disease severity in patients with chronic rhinosinusitis, and whether pharmacologic manipulation of this pathway has therapeutic potential.